Clean Coal, at Last?

By Mark Dwortzan

Guided by a computational model that simulates electrochemical reactions within a solid oxide fuel cell using different candidate materials, ENG researchers will attempt to produce a fuel cell with at least a 50 percent power density improvement over current technology.

In 2011 coal-fired power plants generated more than 40 percent of U.S. electricity—and nearly 80 percent of carbon dioxide emissions produced by the entire electric power sector. One of the National Academy of Engineering’s Grand Challenges for Engineering is to capture and store this carbon dioxide to help prevent global warming, but doing so without driving up the cost of electricity is no easy task.

Now the Department of Energy is awarding $3.5 million to seven university-based research teams across the country—including one from Boston University—to spend the next two years advancing fuel cells that generate efficient, cost-competitive electricity from domestic coal with near-zero emissions of carbon dioxide and air pollutants. Fueled by gasified coal, such fuel cells could automatically capture up to 99 percent of carbon dioxide emissions while emitting virtually none of the nitrogen and sulfur oxides (major components of smog) produced by coal-fired power plants.

Building on six years of previous, DOE-funded research, the BU team—Associate Professor Srikanth Gopalan, Professors Soumendra Basu and Uday Pal, and Assistant Professor Xi Lin (all ME, MSE), and Professor Karl Ludwig (Physics, MSE), along with multiple graduate and undergraduate students—is tasked to demonstrate a 50 percent improvement in maximum power density—watts per square centimeter of electricity produced—of solid oxide fuel cells. To achieve this goal, they plan to use new, lower-cost, higher-performing materials and a variety of experimental and computational tools.

“Clean energy research today tends to focus on renewables such as solar, wind, hydro, wind and biofuels, but they’re still a long way off in providing high-efficiency power generation systems,” said Gopalan, the project’s principal investigator. “By increasing the efficiency of coal and other fossil fuel-based systems, we can decrease the carbon dioxide emissions that they produce and the cost of generating electricity from them.”

Upgrading the Solid Oxide Fuel Cell

Structured like a battery, a fuel cell has four main components: a cathode, or positively-charged terminal; an anode, or negatively-charged terminal; an electrolyte, or substance that can conduct ions, or charged particles, between cathode and anode; and an interconnect, which links each fuel cell with an adjacent one in series, so the electricity each generates can be combined. The function of each fuel cell is to convert chemical energy from fuel such as hydrogen or methane into electrical energy through controlled reactions between the input fuel and air.

Rather than using liquid electrolyte typically found in batteries and many fuel cells, the five-square-inch solid oxide fuel cells (SOFCs) that the BU team is developing exploit a thin, translucent ceramic membrane made of zirconium oxide to conduct oxygen ions from cathode to anode. To build a lower-cost, higher-performing SOFC, the team seeks new materials for the cathode that result in higher performance at lower operating temperatures. Such materials would enable the replacement of the current interconnect material with a much cheaper, off-the-shelf material such as ferritic (iron-containing) stainless steel, which is prone to rust formation at typical (over 800 degrees Celsius) SOFC operating temperatures.

Guided by a computational model that simulates electrochemical reactions within the cell using different candidate materials, the researchers will conduct experiments that test promising cathode materials in a fuel cell for improved power density and durability.

“We’re also expected to deliver to the DOE an actual cell with at least 50 percent performance improvement at lower temperatures,” said Gopalan. “We’re one of the few teams in this program to make a fuel cell from concept to fabricated device.”

The BU project is managed by the Office of Fossil Energy’s National Energy Technology Laboratory through a Solid State Energy Conversion Alliance (SECA) grant. Founded in 1999, SECA is a collaboration among the federal government, private industry, academic institutions and national laboratories devoted to the development of low-cost SOFC technology.